Author
Topic: What's new in Antarctica ? (Read 168614 times)

I just want to draw some attention to a future calving in East Antarctica. I don't know the name of the ice shelf but it's the one directly west of Roi Baudouin Ice Shelf. Big calvings in this area seem to be rather rare.

Also a very interesting region to watch is around the southern part of the Wilkins Ice Shelf (and its neighbours). The cracks in the picture (Beethoven Peninsula at bottom) will eventually help to break up Wilkins Ice Shelf completely within the next years.

... Pure ice is blue because ice absorbs more red light than blue light. Most icebergs appear white or blue when floating in seawater, but since the early 1900s explorers and sailors have reported seeing peculiar green icebergs around certain parts of Antarctica.

The green icebergs have been a curiosity to scientists for decades, but now glaciologists report in a new study that they suspect iron oxides in rock dust from Antarctica's mainland are turning some icebergs green. They formulated the new theory after Australian researchers discovered large amounts of iron in East Antarctica's Amery Ice Shelf. Watch a video of the new findings here.

... Published this month in the journal Geophysical Research Letters, the study analysed daily Antarctic snowfall data starting in the 1970s. It reveals how the most extreme 10 percent of snowfall events account for up to 60 percent of annual snowfall in some places, and are the result of a few large storms that develop over the Southern Ocean.

In one particular case, 44 percent of annual snowfall occurred in a single day. Understanding the significance of these events is critical for scientists interpreting Antarctica's past, as well as predicting how our climate may behave in future.

... "They are often short-lived events, which arrive suddenly and deposit a large fraction of the year's snowfall. If you are an ice core scientist trying to decipher messages from our past climate, and predict the future, knowing about these extreme weather events can be the missing part of the jigsaw." ...

Australian researchers have discovered huge underwater lakes beneath the largest glacier in east Antarctica.

The lakes were detected by scientists setting off small explosives 2m below the surface of the Totten glacier and listening to the reflected sound. The Totten glacier is 30km wide and up to two kilometres thick, and has the potential to raise sea levels by seven metres

“This study has shown us for the first time that there are substantial amounts of water contained in subglacial lakes, not far from the ocean, that we know very little about.” AAD glaciologist Dr Ben Galton-Fenzi said in a statement.

Thanks, good article, except when it compresses catchup time to 300 years (I've heard 10,000 which may be optimistic, but 300? not if one listens to scientists (though they're only talking about 10-20 meters, and perhaps that's likely) The total rise I've heard for entire ice melt (which a warm Antarctica would imply) is more like 65 meters.

Quote

Temperatures may currently be lower than in the Pliocene, but that's only because there is a lag in the system

The Antarctic Bedrock data was over 10 times harder to align than Greenland. There are hardly any landmarks, just plain white and with fast ice or ice shelfs you don't even know where the land begins. I had to use huge area images to align islands and then cut it down to individual glaciers. The bedrock resolution is just 1km/px as opposed to 0.15km/px for Greenland data.

You can see how the Pine Island and Thwaites bedrock dips away from the ocean. I wonder how quickly the grounding lines will retreat once warmer dense seawater reaches the reverse slope. Warmer salty water flows down that slope, meeting the grounding line, freshens from melting and mixing with the glacial ice water and then flows up the underside of the glacier from the increase in buoyancy? A rather terrifying thermodynamic instability.

"Geodetic investigations of crustal motions in the Amundsen Sea Sector of West Antarctica, and models of ice-sheet evolution in the past 10,000 years have recently highlighted the stabilizing role of solid Earth uplift on polar ice sheets. One critical aspect, however, that has not been assessed is the impact of short-wavelength uplift generated by the solid Earth response to unloading over short time scales close to ice-sheet grounding lines (areas where the ice becomes afloat). Here, we present a new global simulation of Antarctic evolution at high spatiotemporal resolution that captures all solid Earth processes impacting ice sheets and show a projected negative feedback in grounding line migration of 38% for Thwaites Glacier 350 years in the future, or 26.8% reduction in corresponding sea-level contribution.The specific processes involved in this negative feedback have previously been extensively investigated, such as self-attraction and loading (SAL) (1), rotational feedback (2) and redistribution of mass in the Earth due to Glacial Isostatic Adjustment (GIA) (3, 4). Some of these processes, SAL and GIA in particular, have been shown to stabilize grounding line retreat of ice sheets resting on retrograde slope (5–7). Geodetic investigations of crustal uplift in the Amundsen Sea Sector (ASS) ( and models of grounding-line retreat followed by re-advance in the Ross Sea Sector during the past 10,000 years (9) have recently confirmed the stabilizing role of solid-Earth deformation. Our focus here is however on how short-wavelength uplift generated by the unloading of the Earth crust over short time scales in the immediate vicinity of grounding lines further impacts the dynamics of ice-sheets grounding-line migration. This particular aspect has not previously been investigated. Indeed, grounding lines in Antarctica are geographically refined features that need to be spatially resolved at resolutions below 1 km (10), and that migrate over short time scales (weeks to month) (11), which triggers the question of how to avoid underestimating the resulting uplift upon migration. Our global simulation of Antarctic evolution presented here is carried out at the necessary high temporal resolution (14 d and 365 d for the ice and solid Earth, respectively) and spatial resolution (1-50 km) required to capture the processes stabilizing and destabilizing ice sheets. These include interactions that involve global eustatic sea-level rise (SLR), SAL, elastic rebound of the solid Earth and rotational feedback.In Antarctica, dynamic retreat of ice streams has been the main driver of mass loss (12). These ice streams are largely controlled by how their grounding lines migrate (13) and interact with pinning points (14). Recent research efforts have focused on the complex interactions between intrusion of warm circumpolar water near the grounding line (11), ungrounding of pinning points (14, 15) and reduction in buttressing through loss of friction (16). A key aspect of understanding grounding-line dynamics (GLD) is to understand the relationship between the evolving sea level relative to the exact position of pinning points. As shown through NASA’s Operation IceBridge topographic mapping as well as decades long efforts to map grounding-line migration, highly resolved pinning points are present in critical areas of WAIS that can only be captured at kilometer scale resolutions (17, 18). In parallel, studies have shown that the physical representation of grounding line migration can only be modeled through meshes that attain 1 km resolution (19). There has been recent interest in developing future projections of SLR that incorporate solid-Earth processes with Maxwellian viscoelastic response (5, 6, 20) and SAL (5, 21). However, these tend to involve GLD that is resolved at much coarser resolutions (25-100 km) and involve time steps on the order of years or even decades. Such resolution bounds are incompatible with capturing the complex geometry of WAIS ice streams that are vulnerable to rapid retreat. For example, Pine Island Glacier (PIG) is 20-30 km wide at the grounding line, with complex grounding-line geometry that can only be resolved spatially at the 1-2 km level (10). In addition, a resolution of 25-100 km is inherently too coarse to capture short wavelength elastic uplift generated by fast grounding-line retreat and associated mass loss. As shown in Fig. 1, elastic uplift generated by a 2 km grounding-line retreat, modeled as loss of 100 m thick ice from a disk of 2 km radius, can reach 52 mm near the grounding line (centroid of the equivalent disk). At coarser resolutions (say, 16 km) the same model generates uplift one order magnitude lower. This implies that uplift generated in simulations such as (5, 6, 20) might underestimate how much uplift is generated during ungrounding of active areas of Antarctica such as TG or PIG, where highly complex grounding line geometries and associated retreat are observed over short time scales on the order of years. Some models such as (22) have attained resolutions down to 6 km, however in such cases GLD has not been considered interactively but prescribed offline, which precluded extensive negative feedback from manifesting themselves during the simulations. Our goal here is to carry out a sensitivity study of sea-level and ice-flow related processes by incorporating kilometer scale resolutions and global processes that involve solid-Earth dynamics. The ice-flow model robustly captures grounding line dynamics at high resolution (1 km) and over very short time scales (2 week"

I have just a maybe stupid question concerning the uplift:¤ If ice sits on land above sea level and if it melts, I expect an uplift of the land afterwards according to the lost weight.¤ If ice sits on land below sea level and if it is completely replaced by ocean water, then I expect an uplift only of the parts that had been icy above sea level before, because all ice that had been there below sea level is now replaced by water (I assume identical density of water and ice for an easier estimation).¤ If ice sits on land below sea level and if it is only partially replaced by sea water (in the case of a grounding line retreat and the formation of an ice shelf) is there any weight loss (apart from a possible thinning of the ice shelf)?

I think uplift is affected by the loss of ice that was above sea level. But when the grounding line retreats and an ice shelf forms, almost by definition the total thickness of the ice decreased such that some ice was lost above sea level. Otherwise the ice mass would sink back to the grounding line.

"As shown in Fig. 1, elastic uplift generated by a 2 km grounding-line retreat, modeled as loss of 100 m thick ice from a disk of 2 km radius, can reach 52 mm near the grounding line (centroid of the equivalent disk)."

In the quoted example the change in the slope due to grounding line retreat is 26 parts per million. That surface tilt is so slight that a drop of water might take a while to figure out which way was downhill on a flat piece of glass so tilted off the horizontal. Such a change in slope is well below the precision of current icestream bed slope measurements, so the hypothesis cannot be tested.

This seems at odds with the authors' claim:"show a projected negative feedback in grounding line migration of 38% for Thwaites Glacier 350 years in the future, or 26.8% reduction in corresponding sea-level contribution."

Also, the analysis apparently also ignores bed roughness and MICI, for the glacier can be supported while it calves, and then can thin rapidly with fast grounding line retreat.

The authors spent more time on this than I have. Am I overlooking something basic?

Maybe this can help clarify things. Most of the effect is later in the simulation - this ain't gonna save us. (And of course these gravitation and uplift feedbacks are not new, they are just better quantified in this paper).

Quote

The negative feedbacks from SAL and elastic uplift for WAIS are significant, but not unique to the area. Because our model runs are global, the same analysis can be shown for the entire continent in fig. S4, showing negative feedbacks in areas of strong retreat, such as the tributary ice streams of the Ronne and Ross ice shelves (S6 and S5). However, the impact in WAIS is particularly significant because of the existing retrograde slope of the bedrock and the presence of a prominent bedrock trough upstream of TG, which triggers marine ice-sheet instability (24) and results in significant ice thickness change rates upon ungrounding. In addition, strong ice/ocean interactions are captured for this area in our melt rate parameterization under the TG ice shelf (11). The melt rates computed for this area are much larger (reaching highest values of 60-80 m at the grounding line) than for other areas in Antarctica (35). The rate at which TG loses mass to the oceans starting year 2250 is strong enough as to generate changes in surface velocity of 3 km/yr inland (figs. S11 and S12), resulting in dynamic changes in surface elevation of up to 45 m/yr by 2500 (figs. S13 and S14). The changes in ice load are responsible for generating elastic uplift on the order of 3-5 cm/yr by year 2100-2300, increasing to more than 20 cm/yr at the onset of TG’s dynamic retreat, culminating at 45 cm/yr around year 2500 (figs. S15 and S16). This uplift rate generates large differences in the vertical position of the bedrock along TG flowlines (see flowline profile in Fig. 4) on the order of tens of meters. The uplift rates have been independently validated (fig. S17) using a benchmark experiment (36).

Logged

magnamentis

perhaps one can put into account that even if we have, let's say for example, an uplift of 5 meters, and at the same time we have a sea-level rise of > 5 meters, that would make the water edge remain in vicinity of where it was before and not much would change in that aspect. just mentioning it as a factor without specific knowledge or opinion as to non-effects

Maybe this can help clarify things. Most of the effect is later in the simulation - this ain't gonna save us. (And of course these gravitation and uplift feedbacks are not new, they are just better quantified in this paper).

Quote

Agree this will not save us and this article is a better quantification of already known factors related to isostatic rebound

... Such resolution bounds are incompatible with capturing the complex geometry of WAIS ice streams that are vulnerable to rapid retreat. For example, Pine Island Glacier (PIG) is 20-30 km wide at the grounding line, with complex grounding-line geometry that can only be resolved spatially at the 1-2 km level (10). In addition, a resolution of 25-100 km is inherently too coarse to capture short wavelength elastic uplift generated by fast grounding-line retreat and associated mass loss. As shown in Fig. 1, elastic uplift generated by a 2 km grounding-line retreat, modeled as loss of 100 m thick ice from a disk of 2 km radius, can reach 52 mm near the grounding line (centroid of the equivalent disk). At coarser resolutions (say, 16 km) the same model generates uplift one order magnitude lower. This implies that uplift generated in simulations such as (5, 6, 20) might underestimate how much uplift is generated during ungrounding of active areas of Antarctica such as TG or PIG, where highly complex grounding line geometries and associated retreat are observed over short time scales on the order of years. Some models such as (22) have attained resolutions down to 6 km, however in such cases GLD has not been considered interactively but prescribed offline, which precluded extensive negative feedback from manifesting themselves during the simulations. Our goal here is to carry out a sensitivity study of sea-level and ice-flow related processes by incorporating kilometer scale resolutions and global processes that involve solid-Earth dynamics. The ice-flow model robustly captures grounding line dynamics at high resolution (1 km) and over very short time scales (2 week"

There seems to be no support for 'short wavelength elastic response'. The earth does respond to loads elastically, the classic work being done on the loading of the Hawaii by A. B. Watts, but the wavelength of the response being dependent on the effective elastic thickness of the lithosphere (Te). My work on Africa showed that the continental lithosphere elastic loading response is more constrained by the current heat flow through the lithosphere rather than it's age. You would expect an elastic response to unloading, and the Antarctic rift would more than likely have a low Te, so relatively short wavelength. However, elastic and loading and unloading is constrained by how quickly rock can respond, and fails by brittle failure at the surface or undergoes ductile flow at the base of the elastic plate. The authors saying that there will be 5cm uplift by the movement of the grounding line as the ice melts, and that this response is on a decade timescale.. If we were seeing an elastic response at short wavelengths such of this, rapidly generating large rates of uplift with high curvature I would think you would see seismic activity all along the the grounding line as the upper crust fails and undergoes normal faulting. It would be interesting to know what effective Te was used to model this uplift, but it isn't mentioned in the paper. This might be happening, but if the earth was responding that fast I think it would be observable.

Rox, are you suggesting that, if the authors are correct about the rebound mechanism, the ice volume loss outcome would be likely to be dominated by an increase in geothermal energy delivery to the Glacier?

I'm not suggesting changes in thermal activity, West Antarctica has high thermal flows, and likely to have a low elastic thickness because of it. Unloading might reduce pressure on existing magma chambers, and cause an increase in volcanism, but that's been discussed elsewhere.

I am aware of the existing high thermal flows; I think of volcanism as a fast thermal flow. I'm naive here, as my posts probably show. Are you suggesting that the scenario projected by Larour, etc. would likely be interrupted by volcanic activity?

Their hypothesis is that they can model visco-elastic rebound of the grounding line using unloading of a disk of ice, and proposing rapid (5cm a year) uplift of rocks as the weight of the ice load is removed. I'm speculating that there would be seismic activity if the lithosphere were to respond rapidly and locally to any unloading as existing faults activate to take up the strain (and the vector of movement along those faults would be consistent with the uplift).

I made some Glacier size comparison charts featuring Greenland & Antarctic Glaciers. I hope it better visualizes how much ice is exposed to ocean water than a Bedrock map. The charts shows the dimensions of the glacier front. Where the x-axis is the glacier width and the y-axis is the glacier height.

The visualization is great but I have some questions:At what cross-section was the data measured? At the grounding line?Is PIG really that wide? I thought it was 40km.And some of the heights seem strange. Petermann, NG and even PIG could float with these heights.

The visualization is great but I have some questions:At what cross-section was the data measured? At the grounding line?Is PIG really that wide? I thought it was 40km.And some of the heights seem strange. Petermann, NG and even PIG could float with these heights.

The Grounding line isn't very smooth and changes constantly. I did just draw a line behind the glacier terminus where the bedrock is more or less a valley. Pretty much all of the west antarctic region is below sea level. You can't use below sea level as a definition, because then Pine Island and Thwaties are the same glacier.

Yes, Petermann, NG and PIG all float at the terminus. Do you think another thickness line would fit into the graphs? It's already quite crowded and the thickness data is even more unreliable / out of date.

PIG 40km is about right for the flat floating part, but not the whole valley which includes ice from the sides coming down.

Scientists from the University of Edinburgh, UK, created this new view by processing data from ESA’s CryoSat in a clever way. CryoSat carries a radar altimeter that measures the height of the world’s ice. Typically, the data are used to map the height of ice at single points. And, since it was launched in 2010, this has revealed much about how ice sheets, glaciers and sea ice are changing.

Nevertheless, a technique called ‘swath processing’ takes the data to a new level. Scientists have used CryoSat’s novel ‘interferometric mode’ to produce whole swaths of data and in much finer detail and faster than is gained by conventional radar altimetry. The usual spatial resolution of a few kilometres has been improved to less than one kilometre.

The technique is allowing scientists to better understand change and predict how ice sheets, glaciers and ice caps may behave as climate change takes a stronger grip. This is important with respect to global concerns such as sea-level rise.

The team used this method to map Greenland in 2017, and now the Antarctica model is available. Both datasets can be downloaded from the CryoTop website.

... A study published in the journal JGR Oceans revealed for the first time that deep water driving melting at the base of the Totten Glacier is warmer and in a thicker layer during winter and autumn than during spring and summer.

Lead author Alessandro Silvano, from IMAS, said this means the Totten Glacier might melt more rapidly in winter than summer, and that summer measurements might under-estimate the flow of warm water to the ice shelf.

... "We immediately noticed that the ocean was warmer in autumn and winter than found in our previous summer measurements. "The new measurements confirm that this part of East Antarctica is exposed to warm ocean waters that can drive rapid melt, with the potential to make a large contribution to future sea level rise.

"The floats also provided new measurements of ocean depth in the region, revealing a deep trough that allows warm water to approach the glacier year-round," Mr Silvano said.

I think that the ozone hole is related to Antarctica, so maybe the best topic for this post is this one.

Mysterious spike of ozone-destroying chemical is traced to east China

Quote

A troubling spike in emissions of a globally banned chemical that damages the Earth’s protective ozone layer has been traced to two provinces in eastern China, according to a study published Wednesday that has alarmed scientists who monitor the planet’s atmosphere.The study, published in the journal Nature, comes one year after another report revealed that air samples had shown a startling excess of a type of chlorofluorocarbon known as trichlorofluoromethane, or CFC-11, since 2012.This manufactured chemical, once widely used to blow polyurethane into a rigid insulating foam, leaks into the air and destroys ozone molecules in the upper atmosphere. The ozone layer is critical to life, limiting the amount of harmful ultraviolet solar radiation that reaches the planet’s surface. CFC-11 is also a potent greenhouse gas, with roughly 4,750 times the heat-trapping potential of carbon dioxide.

The British Antarctic Survey has now published a map in which seven glaciers were named after satellite missions whose data made a decisive contribution to the exploraiton of ice mass changes. In addition to GRACE, for example, Landsat, Envisat and Cryosat were also eponymous. The scientific evaluation of the GRACE mission was led by GFZ German Research Centre for Geosciences and the US Space Agency NASA.

The newly named glaciers are located in Western Palmer Land, next to the George VI Ice Shelf. The name is based on a work by the British scientist Anna E. Hogg from 2017. The polar researcher had demonstrated the acceleration of ice movements in the British part of Antarctica using numerous satellite data. Until now, the glaciers she studied were only called by numbers, not names.

« Last Edit: June 07, 2019, 08:08:08 PM by vox_mundi »

Logged

“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

Warming waters in the western tropical Pacific Ocean have significantly increased thunderstorms and rainfall, which may affect the stability of the West Antarctic Ice Sheet and global sea-level rise, according to a Rutgers University-New Brunswick study.

Since the mid-1990s, West Antarctica—a massive ice sheet that sits on land—has been melting and contributing to global sea-level rise. That melting has accelerated this century. Wind and weather patterns play a crucial role in governing the melting: Winds push warm ocean water toward the ice sheet and melt it from below, at the same time as winds bring warm air over the ice sheet surface and melt it from above.

The study, in the journal Geophysical Research Letters, found that the South Pacific Convergence Zone, a region of the western tropical Pacific, is a major driver of weather variability across West Antarctica.

Rutgers researchers studied how warming ocean temperatures in the western tropical Pacific influence weather patterns around West Antarctica. This century, the Antarctic Peninsula and interior West Antarctica have been cooling while the Ross Ice Shelf has been warming—a reversal of what happened in the second half of the 20th century. From the 1950s to the 1990s, the Antarctic Peninsula and interior West Antarctica were the most rapidly warming regions on the planet, and the Ross Ice Shelf was cooling.

The temperature trends flipped at the start of this century. Coinciding with the flip in West Antarctic temperature trends, ocean temperatures in the western tropical Pacific began warming rapidly. Using a climate model, the researchers found that warming ocean temperatures in the western tropical Pacific have resulted in a significant increase in thunderstorm activity, rainfall and convection in the South Pacific Convergence Zone. Convection in the atmosphere is when heat and moisture move up or down.

A rainfall increase in the zone results in cold southerly winds over the Antarctic Peninsula and warm northerly winds over the Ross Ice Shelf, consistent with the recent cooling and warming in those respective regions. So the West Antarctic climate, although isolated from much of the planet, is profoundly influenced by the tropics. The findings may help scientists interpret the past West Antarctic climate as recorded in ice cores.

AbstractSatellite imagery is used to show that the world's second largest emperor penguin colony, at Halley Bay, has suffered three years of almost total breeding failure. Although, like all emperor colonies, there has been large inter-annual variability in the breeding success at this site, the prolonged period of failure is unprecedented in the historical record. The observed events followed the early breakup of the fast ice in the ice creeks that the birds habitually used for breeding. The initial breakup was associated with a particularly stormy period in September 2015, which corresponded with the strongest El Niño in over 60 years, strong winds, and a record low sea-ice year locally. Conditions have not recovered in the two years since. Meanwhile, during the same three-year period, the nearby Dawson-Lambton colony, 55 km to the south, has seen a more than tenfold increase in penguin numbers. The authors associate this with immigration from the birds previously breeding at Halley Bay. Studying this ‘tale of two cities’ provides valuable information relevant to modelling penguin movement under future climate change scenarios.